[sdiy] Analogue LFOs with Skew and Sync

ackolonges fds ackolonges at hotmail.com
Sat May 23 08:15:52 CEST 2020

Hi Pete,

Thanks a lot for the suggestion. I actually have a couple of those Thomas Henry XR-2206 'El Cerrito' VCOs, so I took a look at their output on the oscilloscope to see if they could be repurposed in such a way. Unfortunately in the case of these VCOs the 'skewing' is a rotation of the descending edge of the triangle, resulting in a sawtooth an octave higher, rather than the usual LFO definition of skew, which is a sawtooth on one side, tilting to a triangle in the middle, and a ramp on the other side.

Also running the VCO at LFO frequencies is giving me a quite different shaped waveform, and the sync, while working, is not quite working in the way I'd expect it to work with an LFO (it's disrupting the continuity of the waveform but giving inconsistent starting points). Though these results may be due to my VCOs being out of calibration or something.

From: Pete Hartman <pete.hartman at gmail.com>
Sent: Saturday, May 23, 2020 4:35 AM
To: ackolonges fds <ackolonges at hotmail.com>
Cc: Synth-Diy mailing list <synth-diy at synth-diy.org>
Subject: Re: [sdiy] Analogue LFOs with Skew and Sync

Thomas Henry's El Cerrito VCO was able to do VC skew, and while it's not an LFO per se, it is capable of reaching LFO rates and in fact the version I built had a switch for LFO mode.

On Fri, May 22, 2020 at 8:37 AM ackolonges fds <ackolonges at hotmail.com<mailto:ackolonges at hotmail.com>> wrote:
Hi All!

You may or may not remember me asking about analogue LFOs with VC-Skew not too long ago, and a lot of you provided really useful references and help. Thanks for that!

Well, I'm still working on my ideal LFO, and I'd like it to have a 'sync' or 'reset' input. I've looked at a whole bunch of different analogue LFO designs out there and have so far found that they seem to *either* have skew ability, *or* sync, and I've so far been unable to get a 'skew-core' LFO to sync properly in simulation (which I'm defining as 'resets to 0v, and continues in the positive direction from there upon receiving a trigger signal').

Does anyone know of any analogue LFO designs that have both skew and sync capabilities, or have any ideas relating to that?
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